This is the iOS version that adds WebGL 2 support. (https://webglreport.com/?v=2)
It'll make it easier to make cool sites, but I wouldn't expect any change in the games landscape. Plus it really looks like the 30% isn't here to stay.
This is what our startup has been focused on for Unreal Engine 4 to target WebGL. We've achieved scenes that are sub 10MB that load in up in two seconds in the browser on most devices.